1. Field of the Invention
The present invention relates to audio video products. More particularly, the present invention relates to methods for encoding video and audio in external processors connected with a host computer.
2. Description of the Related Art
With the advancements in imaging technology and increased computer processing power, much attention has been focused on the acquisition and processing of audio/video data in personal computers. Currently, video sources provide audio and video data in either or both of analog and digital formats. In order to facilitate the processing of video signals by computers, video boards having image acquisition capabilities are used.
These boards may be internal or external to the PC and typically accept a video signal in either an analog or digital format and transmit the signal in a digitally encoded format to the computer. Analog signals, in particular, require conversion to a digital format and in many cases compression before the data is transmitted to the host computer. Analog video signals are typically organized into frames. In the United States and other compatible countries NTSC signals are transmitted typically at 30 frames or 60 fields per second. In other parts of the world, for example in PAL systems, the video signals are transmitted at 25 frames or 50 fields per second. An analog to digital converter (ADC) digitizes the incoming video and audio signal in response to synchronization information embedded in the analog video signal.
The resulting digitized frame samples are temporarily stored in a frame acquisition buffer and then transferred to the computer system memory for further processing. In contrast, a digital video source (e.g., a digital camcorder) provides a digital video signal to the video board via the digital video port. Since the digital video signal already comprises a stream of digitized video frames, the ADC on the video board is bypassed and the digitized frame data is forwarded directly to the frame acquisition buffer in the board.
In both cases, the data is available to the host computer processor via a communications cable. The communications cable may be an internal bus or an external bus. Further, it may be compressed in a standard format, such as MPEG, before transmission to the host computer. The audio signal is also converted where necessary to digital formats and stored in a synchronized manner with the stored digital video data frames.
With the increase in processor speeds available in consumer PC's, consumer non-linear video editing applications have become more prevalent. Non-linear video editing refers to the process of editing a video file by converting the video to a series of video segments that can be accessed in a non-linear (e.g., random) manner. Typically the video signal and its various video segments are stored in a digitized form on a hard disk. The edited video is then reassembled by accessing the selected video segments as well as effects, and transitions.
Often, video capture boards are add-in boards available for insertion into an internal bus of a PC. In some cases, the video capture add-in board is available as a peripheral, connected to the PC over an external bus. External busses such as the Universal Serial Bus (USB) and/or the IEEE-1394 Bus are increasingly found on consumer PC's.
Video editing typically involves high speed busses and high capacity storage. Raw video significantly increases the demands on the busses and storage in comparison to compressed video. Hence, most video captured is compressed, i.e., encoded before the digitized video is transmitted to the host computer for editing.
DV-25 is a common compression format used for video. This format involves intra-frame compression which makes it especially suitable for many editing applications. Unfortunately, the DV format is not a common consumer distribution format. Typically, videos are distributed in any of several MPEG formats. For example, the VCD format employs an MPEG-1 compression scheme and enjoys popularity in many parts of the world, especially Asia. MPEG-2 provides an even higher resolution and even greater popularity when stored on optical DVD's (Digital Versatile Disks). Accordingly, many consumers have a desire to convert edited video in the DV-25 format into one or more consumer distributable formats.
Even with the availability of increased PC processor speeds, the process of transcoding, i.e., converting the videos from one compression format (e.g., DV-25) to another (e.g., any of the MPEG formats), is both a time consuming and a processor intensive task, typically performed in a software encoder in the host computer.
It is therefore desirable to provide an improved device for transcoding video from one video format to another.